1. Field of the Invention
The present invention relates to a motor drive circuit adapted to control the rotation speed of a motor in a variable manner.
2. Description of the Related Art
Recently, OA (office automation) devices, such as copying machines, page printers, and the like, have been and being developed more and more with colorization, enhanced definition and digitization, and accordingly a motor that is used in those equipment is required to operate in a wide range of rotation speed and also with a high accuracy of rotation speed. In a drive circuit to drive such a motor, it is required to provide an optimum control capability at every rotation speed through the wide range of rotation speed.
Also, as to a driving method to drive such a motor, from a viewpoint of reducing noises, a sine wave driving in which a voltage applied to a motor winding is shaped to have a sine wave form is more and more employed generally in place of a rectangular wave driving conventionally used. It is known that an advance angle control to adjust a delay of the phase of a winding current with respect to the phase of a motor inductive voltage is essential in order to maintain a high efficiency for the aforementioned sine wave driving.
Referring to FIG. 3, a controller 107 is shown as a conventional motor drive circuit which is provided with a function of controlling an advance angle (refer to, for example, Japanese Patent Application Laid-Open No. 2005-192338). The controller 107 shown in FIG. 3 is an example of a motor drive circuit to drive a three-phase brushless motor (hereinafter, referred to simply as a motor) 106 used in a hydraulic power steering system.
The controller 107 includes: a target rotation speed calculating device 173 to calculate a target rotation speed based on inputs sent from a rudder angle sensor 111 and also from a vehicle speed sensor 112; and a rotation speed calculating device 174 to calculate a rotation speed of the motor 106 based on an input sent from a rotation position detecting sensor 171, wherein a deviation between the target rotation speed and the actual rotation speed is fed to a rotation speed controlling device 175. Then, the rotation speed controlling device 175 as well as a PWM controlling device 176 act to set a control voltage by a proportional control and an integral control, whereby the rotation speed of the motor 106 is controlled via a drive circuit 172.
And, in a phase controlling device 177 of the controller 107, an optimum energization phase of the drive circuit 172 is obtained based on control parameters, such as a proportional term, an integral term and the like, which are calculated at the rotation speed controlling device 175, and the result of the calculation is reflected at the PWM controlling device 176, whereby an advance angle control is performed.
Further, another conventional motor drive circuit is proposed, which is adapted to control a rotation speed varying in a wide range, and which is configured such that two advance angle values are predetermined and such that the advance angle values predetermined are switched over by a level High/Low of a voltage applied to an advance angle value setting terminal.
For example, in an advance angle value setting circuit shown in FIG. 4, a High/Low level of a voltage applied to a PS terminal (advance angle value setting terminal) is set by Open/Short (GND) of the condition of a PSO terminal, and a setting of an advance angle value is changed over in response to the switchover of the aforementioned voltage level setting. A signal for switching the condition of the PSO terminal is usually supplied from outside via an interface of the motor drive circuit according to the rotation speed of a motor, or the like.
As described above, the controller 107 shown in FIG. 3 is provided with the target rotation speed calculating device 173 which functions to calculate the target rotation speed of the motor 106 based on inputs sent from the rudder angle sensor 111 and the vehicle speed sensor 112, and also provided with the rotation speed controlling device 175 to which a deviation between the target rotation speed and the actual rotation speed is fed, wherein an advance angle control is performed based on control parameters, such as a proportional term, an integral term, and the like, which are obtained at the rotation speed controlling device 175. Therefore, the advance angle control which is performed in the controller 107 cannot be performed in a motor drive circuit in which a rotation speed controlling device based on a target rotation speed (target speed) is not provided.
Also, in the configuration of such a circuit as shown in FIG. 4, in which an advance angle value is switched over according to a signal level applied to an advance angle value setting terminal, for example, if the number of corresponding advance angle values is to be increased for the purpose of performing a control with a higher degree of accuracy, a complicated switching circuit is required, in which a large number of resistors and switch elements, or the like must be provided.
The present invention has been made in light of the above problems, and it is an object of the present invention to provide a motor drive circuit which is enabled to variably control the rotation speed of a motor, and in which an appropriate advance angle value can be automatically set in accordance with the motor rotation speed.
The embodiment shown in the following description of the invention is presented in order to exemplify a configuration according to the present invention and serves to provide an explanation on an aspect-by-aspect basis for the purpose of facilitating understanding of the diversity of the configuration of the present invention. Each aspect does not limit the technical scope of the present invention, and modifications which, in consideration of the best embodiment mode for carrying out the present invention, are developed by replacing, eliminating a part of the constituent elements of each aspect, or further by adding some other constituent elements thereto may be included in the technical scope of the present invention.
In order to achieve the object described above, according to a first aspect of the present invention, there is provided a motor drive circuit configured to include: an advance angle setting correcting device which has a correction reference cycle predetermined according to a reference advance angle count value and in which a correction amount is calculated as a ratio of the correction reference cycle to a cycle of a detection signal indicating a detected frequency proportional to a rotation speed of a motor and in which an advance angle setting signal is obtained in such a manner that the correction amount is multiplied by a proportionality factor; and, an advance angle setting device in which the advance angle correction value is added to the reference advance angle count value thereby outputting an advance angle setting signal. In the configuration described above, a drive command signal containing a rotation speed information based on a target rotation speed is fed to the motor drive circuit from outside, the rotation speed of the motor is variably controlled in response to the drive command signal, and the detection signal indicating a detected frequency proportional to the rotation speed of the motor is fed to the motor drive circuit from a rotation speed detecting device attached to the motor.
According to the motor drive circuit described in the first aspect, an advance angle value can be automatically corrected depending on the fluctuation of the detection signal fed from the rotation speed detecting device, and therefore the efficiency of driving a motor can be optimized at each rotation speed of the motor running with a rotation speed variation in the motor drive circuit to variably control the rotation speed of the motor.
Also, according to the motor drive circuit described in the first aspect, an advance angle setting is corrected based on the detection signal fed from the rotation speed detecting device, and therefore a target rotation speed does not need to be fed from outside for performing an advance angle control, which eventually results in that the advance angle control of the motor can be performed by a simple and inexpensive motor drive circuit which does not include a rotation speed controlling device adapted to work based on a target rotation speed.
Further, according to the motor drive circuit described in the first aspect, an advance angle setting is corrected automatically depending on the rotation speed of the motor inside the motor drive circuit, and therefore a circuit for switching an advance angle value, an interface for introducing a switching signal from outside, and the like are not required, whereby the efficiency of driving motor can be optimized by a simple and inexpensive configuration.
According to a second aspect of the present invention, the motor drive circuit as described in the first aspect may further include a cycle detecting counter to output a detection cycle count value corresponding to a cycle of the detection signal calculated based on a reference clock, wherein the advance angle setting correcting device has a correction reference count value corresponding to the correction reference cycle and includes a division device to divide the correction reference count value by the detection cycle count value thereby calculating the correction amount.
According to the second aspect of the present invention, the motor drive circuit, in which an advance angle value can be automatically corrected depending on the fluctuation of the cycle of the detection signal fed from the rotation speed detecting device, can be configured as a fully digital processing circuit which does not employ an analog circuit (for example, an integration amplifier, a resistor and a capacitor). The motor drive circuit, especially when formed of an integrated circuit (IC), can be achieved as a high-performance circuit which, by utilizing microfabrication process for building more digital circuits in a small area, can be realized with an IC which has a small chip area and which is available at a low cost.
According to a third aspect of the present invention, in the motor drive circuit as described in the first or second aspect, the advance angle setting correcting device may have a plurality of the correction reference cycles.
According to the motor drive circuit described in the third aspect of the present invention, an optimum advance angle setting correction can be performed flexibly and easily with regards to a motor which runs with a wide range of rotation speed variation.
According to a fourth aspect of the present invention, in the motor drive circuit as described in any one of the first, second and third aspects, the rotation speed information contained in the drive command signal may be either a voltage command signal corresponding to the target rotation speed or a PWM duty command signal.
The motor drive circuit according to the present invention is configured as described above and therefore enables, while variably controlling the rotation speed of a motor, to automatically set an appropriate advance angle value in accordance with the motor rotation speed and thus to optimize the efficiency of driving the motor.